Answer: By sending you pictures of them.
In an effort to curb the number of lost letters in the mail, the United States Postal Service (USPS) is introducing a program that will send you images of the letters you should be receiving in the mail each day.
Called Informed Delivery, users have to go to the program page on USPS’ website in order to sign up. They will then receive a confirmation letter in the mail (it's unclear if they will receive a photo of this letter ahead of time). After that, they will receive images of any letters addressed to them that are being delivered that day.
The images can be sent via email, text, or through the USPS Mobile smartphone app. Currently, only letter-sized envelopes will be photographed, so for now you’ll still have to rely on old-fashioned tracking to determine when your expected packages will be delivered.